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Old Feb 05, 2013, 02:11 AM
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Well, for now I have one super clean running fan in the Su..... and one that is more typically 'pretty good'. Twins, especially if the fans are close to each other, need better setting up or else you get terrible sound interactions.
I can't work out what the 'limitation' is in getting it perfect and that was the best initial motor/fan unit before.... When I redid the 'less good' one I got it to be 'fantastic', and that other one got left behind!
These are 3.17mm motor shaft HET's, so that is a part (or the actual) issue. Shaft flex. A 4mm shaft would probably have both of them being 'fantastic' as they are now. Annoying.....

I am going to get a pair of CyclonePower IR550-2200-40's to run in CS12's and replace the HET/CS10's anyway. Then the HETs can go as single fan units into other aircraft I am moving up from 5S to 6S. Less critical as a single unit then - no harmonic reverberations across two fans.

But I want to run up the HET's in the Su again to see all the numbers, as the CP's will be near identical anyway. (I have not ordered the CP's yet as the new CP 12blade alloy housing is coming out any day now, so I will get those all together)
Solo on the bench 65Amps for 1.9Kg thrust (after coming off peak at 70A+ and 2.0Kg+), but that will never be attained in the plane. I will also test them solo, to see them under an easier battery load, as well as the 'proper' both at once for the total number results.
This evening hopefully.... after I TRY a bit more with the 'less good' fan balancing!!

The rotor is balanced the best ever.... with near zero friction magnetic balancing, it just coasts to a stop 'somewhere'. No offset weight or see-sawing etc.
But that isn't a great help if the combo really NEEDS some rotor imbalance, so you can 'clock it all out' to be zeroed.
I tried that too..... took weight off.... re-clocked..... added more.... re-clocked.... but those cases only got worse! So I went back to perfect balance, and clocking that can go to 'worse' positions, but none arrive at 'perfect'.... which seems odd.

I was thinking there could be 'aerodynamic imbalance' in the fan itself. Blade variation, flaw, chip etc (they even often come with micro chips on the blades). Something other than a weight imbalance issue.
Probably a small issue, but the 3.17mm shafts cannot hold up against it. 4mm probably would.
When I get the 4mm CP's I can retry them for a reference to prove what is going on. I expect the 4mm shafts would be strong enough to 'erase' that final small issue - by 'brute force rigidity'. hehe

People who use BL32's, with their hefty 5mm shafts, must LOVE those!! You would get PERFECTION in that case! They are a fantastic motor.... probably the best choice really. But cost more too....
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Old Feb 05, 2013, 03:06 AM
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I have been through this before. this is were you need to start 2 plane balancing. If you start to move the weight your using to balance to the front and rear of the hub and spinner you will get different results and little by little you will get it as smooth as my het 3.17mm shaft set up.

If you see here in the video there is zero resonance and this is proven by looking a the less than 1mm blade to shroud clearance.


There is no aerodynamic imbalance in the cs10 cs12 fans, its just your getting the 2 plane balance wrong, I know what I am talking about because this kind of balance used to take my days to get correct, and now it just takes me 2-3hrs because off what I have learned, and now I balance everything that spins.

Change sun 70mm 12 blade fan on 4s Het 2W25 2720KV (1 min 9 sec)
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Old Feb 05, 2013, 03:41 AM
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yup, everyone talks about dynamic balance, but only a hand full of people actually do it.
Balancing a spinning fan isn't dynamic balance, multi-plane is.

And it's probably what's stopping you getting that final few gmm's of imbalance out.

Think of having a Z shaped piece of wire, with the shaft running vertically. Statically it's balanced, but as soon as you spin it, it'll go nuts. Only way to correct that is to balance in two or more planes.
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Old Feb 05, 2013, 03:52 AM
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Quote:
Originally Posted by Odysis View Post
yup, everyone talks about dynamic balance, but only a hand full of people actually do it.
Balancing a spinning fan isn't dynamic balance, multi-plane is.

And it's probably what's stopping you getting that final few gmm's of imbalance out.

Think of having a Z shaped piece of wire, with the shaft running vertically. Statically it's balanced, but as soon as you spin it, it'll go nuts. Only way to correct that is to balance in two or more planes.
OK, so what exactly is your technique??? I'm curious, because I'm not an expert in this area.

I'd really like to know how to do it........................

P.S. I don't have a cell phone that can run the Android app that has already been mentioned here. Is there another way to do it?????
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Old Feb 05, 2013, 03:52 AM
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Hmmm, I will give that a try......
As much as Tam demonstrates it... it seems (LOL).... in his video and 'super balancer' setup, I can't actually see how it could be that a big a deal.
You have the correct weight already, in the correct position. Typically taking up a few mm at least of distance. If the rotor was so badly made that a lot of the weight error was at the far outer edge, then it is further down the motor shaft and COULD have some effect. If it is towards the hub, the distance to the motor bearing is not great - even at the hub front edge it is just another 12mm approx.
We are talking about a correct overall balance, just with SOME small portion(s) of it fore or aft that small amount.
If the motor shaft was 5mm it would have zero effect, as the shaft is so strong that sort of effect couldn't even exceed the shaft strength.
At 4mm..... maybe even 3.17mm.... it might still not be able to exceed it.
But I could see that it might at 3.17mm.
By 4mm I would think it is becoming neglible effect already.

Tam's 'machine' shows the two plane effects, but what 'numbers' of it really matter? More so at huge powers I expect, but less so at smaller powers. (lower RPMs then) Though this 1300W area is getting to the higher end of powers. But Tam's high ends ones are more to 1600w to 1800w, so RPM is HIGH and things are getting very critical by then... 42K RPM or more areas. It would be notably less important at 38k RPM area.

But maybe it will explain the remaining imbalance. Easy enough to try.
My weights are usually roughly pushed to midway in the hub. But maybe this one had them pushed all the way forwards, or they moved. I use a built up fibre tape 'clump' and it sticks like chewing gum to a blanket! So once it is shoved in it just stays right where it has been put. It does not even 'compress up' outwards due to centrifical force - it stays filling right across the entire 'cell' of the hub. But I will have to double check that one to know for sure....

I guess it should be placed really be where the real weight error was - not really 'two planes', but 'infinite planes' !! ANYWHERE from hub inner edge, to the very forwards end of the hub. So I guess that testing across the whole range could show something up.... as much as I don't really expect to be amazed by it at all.....
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Old Feb 05, 2013, 03:55 AM
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Yeah but a Z piece of wire, that does go nuts, is a BIG amount of 'out of plane' balance.
In our weeny hub and length, that becomes a far smaller factor. The imbalance amount is a very small % of the total rotating mass. In any z-bend it is a large % of that total mass.
It is a true analogy.... just a very extreme case versus ours.
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Old Feb 05, 2013, 04:04 AM
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DOH.... not nice results....

I ran up the one good fan, seeing it is in and ready.
In-Plane it gives 1.48Kg Thrust sustained (for a reasonable while anyway).
That isn't too bad versus 1.9Kg on the bench..... much in the % area of loss I had seen from a few combos in the Su-35 I tried.
The BAD thing, that I have never seen occur before, was that it was 70Amps and 1500Watts!!! That is what it eats to give 1.9Kg/2.0Kg on the bench! Usually in a plane the Thrust falls off, but so do the Amps/Watts.

For the moment I am thinking that it is because the EXHAUST side is the restriction. But I am not really sure....
When it is the inlet side the whole set of result numbers drop off... from Thrust, to Input Power too. In planes I have checked over anyway.
Hmmmm... but I have an F-15 that is a restrictive bifurcated exhaust, plus not large enough area for its larger fan used, and all it does it lower the Thrust AND Power used too. (compared to bench results).
So I am not sure what really happened..... unless the Thrust number (scale) is not truly correct anyway! If the Thrust was really 1.7Kg to 1.8Kg then it woul dbe OK Power numbers.
I have to hook up the KV/RPM meter as a secondary record.....

It sounds very good though. Probably as good as an Su can get with a plastic housed fan. The Su has 'flimsy' inlet side ducting, so there is a lot of flex/motion to allow reverberations in the foam joints etc. but they are minimal.
I guess I should also bolt in and test my Lander 2200kv 6S alloy unit, as a cross reference.....
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Old Feb 05, 2013, 04:16 AM
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It might be a small amount, but if you're chasing that last bit (which you found - one fan easy, another hard...)

I balance the rotor in the 4 run way, with the weight all the way forward. If that doesn't make it smooth enough, I then do it again, but using my test weights on the very back of the rotor.
There is a method out there for proper multi-plane, no phase balancing, but I don't use it.
My method won't perform as well as the 'real' way, but I haven't bothered to read it yet!

The masses need to statically balance the system, as well as provide a couple equal but opposite to the integral of all other couples in the system. If you can do that, in theory a perfect balance is possible (for a rigid system).

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Old Feb 05, 2013, 05:03 AM
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Gee, I don't know... but I have to trust in Tam's outline of "Plane Balancing " at least some amount. Seeing his equipment measures and displays it.
I don't doubt it EXISTS, I just doubt just how much it MATTERS.

I just did some tests....
My weight 'clump' is 4mm 'long'. (DOH, I didn;t WEIGH it!! I will go back out soon...)
I retested the static balance and it is dead perfect... it stops at any point around the rotation. 10 spins.... to verify that.

I then pushed the weight all the way into the hub.... tested the fan. "Clocked" it and there was a least vibration point... which could seem weird if you are rotating a PERFECTLY balanced rotor! (but there is a reason to explain it....)

Then I moved the weight all the way rearwards... the same 'clock' position is optimal. The vibration 'remaining' - which is occuring at a string of harmonic points - is the same.

Then I moved the weight to the mid way..... same results.

No measurable, or perceivable difference... certainly no removal of the harmonics.

So in this case, of my X amount of weight, it shows/suggests it is a neglible effect (the plane of balance)

I believe it is something else.....
Seeing I can rotate a PERFECTLY balanced rotor in the Clock Method and see a DIFFERENCE then that shows there MUST be some change that is occurring when rotating it on the adaptor shaft. There must be some 'error' in there, and it pretty well must be the ROTOR. Seeing no other aspect of the assembly changes.
That means it is either not moulded 1000% accurately - the shaft hole. Or something about the blades is affecting balance via airflow. There could even be "harmonics of airflow disturbance". Or, probably the most likely is just motor housing mount flex in the housing - seeing it is a Freewing plain plastic one. (A CS12 GRP one would be far better!! And Alloy even better!!)
There is nothing else it can be.

If it was 'plane balancing' then the shifting of a weight from one end to the other would show SOMETHING happen..... something measurable, otherwise it is actually a neglible factor. (which it seems to me)

Oh, and Pape.... that video, you have an alloy housing. That instantly gives 1000% gains over a plastic housing as there is then no flex anywhere... rigid motor mount etc. It is far easier... and even possible.... to get 'perfect' balance from an alloy housing. But from the plastic ones.... almost IMPOSSIBLE.
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Old Feb 05, 2013, 05:07 AM
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Oh.... and "two plane" balance....

Over the 10mm of the HUB, that is a very small matter.
But go over from HUB FRONT, all the way to MOTOR REAR - when it is the MOTOR balance that is out - and THEN I would say things are getting to be very comparable to a Z-bend wire!

So if any "Two plane" is coming into things of significance, it will be from THAT longer distance issue.
I expect that would actually be a big issue seen more often in outrunners, which are rarely very well balanced.

When you use the Clock Method, to much greater degree with an Outrunner, you are really offsetting that long distance of motor imbalance via the rotor imbalance. So that really is a "Z-Bend wire" case!!
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Old Feb 05, 2013, 05:15 AM
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The balance weight is 0.13g (using a 0.01g accuracy scale)
I have never actually weighed any before! I would say it is pretty well a typical sort of size 'clump' I need to use.
Though the other fan used a bit less.
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Old Feb 05, 2013, 05:27 AM
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But now more Power perplexing puzzle.....

The test fan in the Su ran at 70Amps and 1500W for 1.48Kg Thrust at 40,000RPM.
The other fan, on the bench, runs at 70Amps 1500W for 1.9Kg Thrust at 40,000 RPM!!!!
The same test equipment is used.

HOW is the in-plane combo running the exact 'on bench' numbers too!!!
I have never seen that happen.

I would say that the Su is one of the 'cleanest' ducting planes I have.... it is almost a straight through 'nacelle' effect.

The Dynam Meteor (Habu clone) is one of the 'nicest' design aircraft around, with very good flow/ducting... but it drops the typical amount of thrust. BUT the Power numbers fall off compared to bench tests too!

The Dynam Me-262, which DOES have nacelles..... loses the typical amount. And again runs at lower Power levels than the potential seen on the bench.

The only way you would really run identical Power numbers to a bench, is if the airflow WAS the same as on the bench! They should never reach that same level in a plane (???).
NOT with the same RPM!!
If it had lower RPM, then the LOAD of the motor could run it into more inefficient areas of operation, and thus Power goes up whilst output Thrust is really lower.

I don't even see HOW a fan can run bench RPM when in a plane!! Unless it was zero restriction.....

To end up at 1.48Kg Thrust instead of 1.9Kg, for the same input power and output RPM, that would suggest to me (but I don't really know) that whilst there was zero back pressure to 'overload' the fan, and thus drop RPM and Power, there must be a CHANGE in the Volume and Efflux speed, versus the bench test.
So the fan is still moving the same amount of air, but the MANNER in which it exits the exhaust nozzle means it gets less 'bite' against the stationary air it is pushing against at the rear. Somewhat like using two different Propeller Diameter and Pitches that both still use the exact same Power and give the exact same RPM from the motor. Identical LOADS, but a different manner of 'pushing' the airflow - one has more speed, the other has more area covered.

I don't really know....
But there is not much else left for logic. Though if there is ever an "unknown" in the data source (not enough info) then that means there are other possible explanations.....
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Old Feb 05, 2013, 05:44 AM
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The next potential problem is going to be the battery feeding TWO fans, wanting 70Amps each!! 30C.... 45C nano... 65C Nano.... none are going to be overly happy about that idea! LOL
I expect to then see them drop to something more like 60A each. Seeing the motor volts will drop due to the higher total battery load.

Then it won't be 1.48Kg per side.... but heading towards 1.3Kg per side.
That is IF the word "THRUST" can even be taken as a constant factor of real USE in claiming what a plane will do!!
"Thrust" is sort of just a reference of what propulsion the 'engines' gave in THAT situation. That static situation, because the way the airflow 'pushes' against air that is out the back of the plane. (That would actually be a true measurement of a plane hovering too!)

Once MOVING the resultants could be different - if comparing two plane's, that use the same power levels (via using different fan types) one with 3.0Kg static thrust and one with 3.4Kg static thrust. I would expect the 3.4Kg one... which you could call the "V8" with high torque (static thrust is actually that).... will not have the top speed of the 3.0Kg one.
It is not a factor of the "X Kg static thrust" number, but of what difference they have in exhaust airflow (efflux speed and volume they each actually do differently). Again exactly like the two propeller cases... same Power in both cases, but one will do higher speeds, the other will have greater 'torque'.

So I am thinking that "Waaah, I only have 2.6Kg total static thrust" is not actually the be all and end all of the situation! Only to someone who cared about torque... generally of use for 3D/Hovering where you WILL need 3.0Kg to hold up a 3.0Kg plane(!!), but not overly important to 'normal' flight cases. The "2.6Kg Static Thrust" plane could very well (likely?) outrun the 3.0Kg one in speed.
There will be a "crossover" point of their performances - much like two drag cars that one gets away faster, but is then caught up and passed by the other further down the strip - so test those two planes against each other and by X amount after take-off they wil be equal, whilst the 3.0Kg Thrust one took off 'faster' initially. Probably crossing over in performance not too long after getting towards the plane's typical cruising speed.

I need a way (we all do!!) to measure EFFLUX SPEEDS also!!

(I happened to weigh my partly assembled Su-35...... Just missing the wings.... AUW 3.1Kg. I don't know what they weigh..... OH!! One EDF missing in that total too!! BAH. This could be heavy in total!! 3.5Kg?)
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Old Feb 05, 2013, 05:51 AM
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wow, 4 in a row - nice!

If moving your 0.13g 'blob' forward and aft doesn't change anything - try adding two 1g 'blobs', 180degrees apart from each other. They won't affect the static balance, but will add a couple. It'll show up eventually!

And I concur - balancing an outrunner, then balancing the rotor is very similar to what I'm talking about, and an example of when a dynamic unbalance is quite noticable.
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Old Feb 05, 2013, 05:53 AM
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I am in "Su mode", LOL.
Since Saturday.....


I am thinking the fan "harmonic" situation is the Freewing plastic housing flex. And possibly the HET motor shaft being some fractional amount weaker than the other motor.
And if they were both 4mm shaft motors... I expect that all would be perfect!!! That exra strength would even help offset/prevent the housing flex some amount too.

I will fly it with these current HET/CS10's first.... and record some numbers in-flight.
Then change to CS12's (HETs) with their stock housings (and pre-test/balance it all of course). These will be V2 with collets!! (yuk). Or I can just keep the screw type adaptors that are on now anyway. (sigh, need to test BOTH!)
Then later change to the CP-IR550's. for their 4mm motor shafts....... THEN into the CP 12blade alloy housing. But that alloy case just more for a static noise/reverberation test as I only really want to use the CS12 stock GRP housing with the CP motors - to save some weight, and $ investment.
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